Mold for making a wedge-shaped polymer



March 1, 1966 E. R. LANG ETAL 3,237,911

MOLD FOR MAKING A WEDGE-SHAPED POLYMER I Filed Aug. 2, 1963 2 Sheets-Sheet l INVENTOR-S'. EDGAR REED LANG I LEWIS C- FOELL ATTORNEY March 1, 1966 E. R. LANG ETAL 3,237,911

MOLD FOR MAKING A WEDGE-SHAPED POLYMER Filed Aug. 2, 1963 2 Sheets-Sheet 2 I I4 ll INVENTORS'. EDGAR REED LANG LEWIS C. FOELL BY ATTOR NEY llnited States 3,237,911 MOLD FOR MAKTNG A WEDGE-SHAPED POLYMER Edgar Reed Lang, Glenside, and Lewis C. Foell, Bristol, Pa., assignors to Rolnn & Haas Compan Philadelphia, Pa., a corporation of Delaware Filed Aug. 2, 1963, Ser. No. 300,141 2 Claims. (Cl. 249-119) This invention relates to the manufacture of plastics in the form of wedge-shaped pieces. More particularly, it relates to a process whereby wedge-shaped plastic pieces are formed by casting. Still more particularly, it relates to molds or cells in which such pieces may be cast or formed and the method of preparing same.

This application is a continuation-in-part of our United States application, Serial No. 215,426, filed August 7, 1962, now abandoned.

It has heretofore been known that flowable polymerizable material may be cast into a rigid sheet of polymer. See, for example, United States Patents Nos. 2,154,639, 2,328,525, and 2,385,486. It has now been found that a plurality of wedge-shaped pieces of polymer can be formed in a cell, such as that used in the casting of sheet, by modifying the cell as hereafter described, thereafter flowing the polymerizable material thereinto, and polymerizing such material.

For a better understanding of this invention reference is made to the accompanying drawing, which illustrates a cell of the type that may be used, and the description which follows.

FIG. 1 is a partially cutaway perspective view of an assembled cell without clamps around its edges.

FIG. 2 is an end view showing one of the two cell walls in a horizontal position and the placement thereupon of conventional flexible mold spacers in parallel, one along each of its edges and one centrally thereof with a sheet of cellophane placed over the spacers.

FIG. 3 is an end view similar to FIG. 2, but showing additional spacers placed on top of the cellophane sheet, a second cell wall placed thereover, and clamps applied along the edges of the cell walls to complete the cell walls to complete the cell assembly.

FIG. 4 is a perspective view showing a typical wedgeshaped piece formed in accordance herewith.

FIG. 5 is an end view similar to FIG. 3, but without clamps, showing a modification of the cell assembly, and FIG. 6 is a view similar to FIG. 5 showing a further modification.

Referring to the drawings in which like reference numerals identify the same parts in the several figures, the casting cell comprises a first cell wall iii and a second cell wall 11 separated by an outer flexible spacer 12 which extends between said walls adjacent three sides of the periphery thereof. As shown in FIGS. 1, 2, 3, and 6 said cell may be provided with one or more additional intermediate spacers 13. Extending diagonally or in a zigzag manner between and held in place taut by the flexible spacers and the cell walls in a sheet of thin, flexible, impermeable material 14. Such sheet may be of suitable gauge cellophane or other flexible, impermeable material. As shown in FIG. 3 the cell is provided around its ends .with suitable clamps 15. A typical wedge 16 produced in accordance herewith is shown in FIG. 4.

The cell, as shown, for example, in FIGS. 1 and 3, is placed in the vertical position with the open edge up. Monomer or a fluid monomenpolymer mix is poured into the spaces between the cell walls and polymerized in 3,Z3?,flll Patented Mar. 1, 1966 the conventional manner. Upon polymerization of the monomer, the cell is disassembled. The resulting polymer is removed as a series of wedge-shaped pieces.

The following example will further illustrate this invention.

Example A cell containing wedge-shaped compartments was constructed as indicated in the drawing referred to above. The walls of the cell were glass sheets. The flexible spacer extending around three sides of the perimeter of the cell was designed to provide a spacing of 0.285" between the cell walls when compressed by the clamps in order to assure a liquid seal. The intermediate dividing spacers were 0.290 in diameter in their noncompressed state. This provided sufficient pressure when the cell was assembled .to form the cellophane divider sheet into a series of compartments without causing undue resistance to the movement of the cell walls toward each other during polymerization after the cell has been charged with polymerizable material. Openings were provided at the lower ends of each compartment so that the fluid charge could flow from one compartment to the other to equalize the pressure in each section during the filling and polymerization steps.

The cell in a vertical position was charged with a degassed methyl methacrylate mixture prepared as follows:

To monomeric methyl methacrylate there were added 0.025% acetyl peroxide and 0.3% stearic acid, each based on the weight of the methyl methacrylate. This mixture was heated to 35 C. and agitated to provide thorough mixing and solution of the stearic acid. It was then freed of dissolved gases under vacuum and poured into the casting cell, care being taken to avoid entrapment of air in the cell. The uppermost end of the cell was then sealed with a strip of flexible spacer.

The cell and its contents were then placed in a circulating air oven and held at 58 C. for 18 hours, at the end of which time polymerization to a solid state of its fluid contents had taken place. Heat was applied for an additional four hours, in which the temperature was raised in 10 C. increments until C. was reached. The cell was then gradually cooled to 40 C. over a period of two hours, at which time the clamps were removed and the cell walls were parted. Upon removal of the perimeter spacers, the polymer in the form of wedgeshaped pieces resulted.

It will be understood that spring or other types of clamps for holding the cell together may be used instead of the specific type of clamps shown in the drawing. Other modifications, such as stretching the cellophane sheet diagonally in the cell between the spacers at the perimeter and leaving out the intermediate spacers as shown in FIG. 5, as well as the use of thin sheets of flexible material other than cellophane, as will readily suggest themselves to those skilled in the art from what is said above, are within the scope of this invention.

What we claim is:

1. A cell for casting flowable polymerizable material into solid wedge-shaped pieces comprising a pair of rigid cell walls separated by a flexible spacer adjacent the perimeters thereof and having a thin, flexible sheet of impermeable material stretched diagonally across the internal portion of the cell in a direction lengthwise thereof and held in place by means of the flexible spacer and cell walls.

2. A cell as in claim 1 wherein one or more flexible spacers are placed intermediate the outermost flexible spacer and the flexible sheet is stretched between the outer References Cited by the Examiner UNITED STATES PATENTS 12/1866 Wiggin.

4/1930 Mead 25131 XR 2,390,129 12/1945 Shobert 1839 XR 2,867,003 1/1959 Stiles 18-39 3,017,683 1/1962 Huch et al. 25-121 FOREIGN PATENTS 1,053,512 9/1953 France.

I. SPENCER OVERHOLSER, Primary Examiner.

WILLIAM J. STEPHENSON, Examiner. 

1. A CELL FOR CASTING FLOWABLE POLYMERIZABLE MATERIAL INTO SOLID WEDGE-SHAPED PIECES COMPRISING A PAIR OF RIGID CELL WALLS SEPARATED BY A FLEXBLE SPACER ADJACENT THE PRIMETERS THEREOF AND HAVING A THIN, FLEXIBLE SHEET OF IMPERMEABLE MATERIAL STRETCHED DIAGONALLY ACROSS THE INTERNAL PORTION OF THE CELL IN A DIRECTION LENGTHWISE THEREOF AND HELD IN PLACE BY MEANS OF THE FLEXIBLE SPACER AND CELL WALLS. 